What to Make of New Study Finding Antioxidant Supplements Worsen Skin Cancer in Mice

Following up on previous work showing that antioxidant supplements may hasten the spread of lung cancer, researchers from Sweden have now found that antioxidant supplements may double the spread of malignant melanoma—the most serious type of skin cancer—in mice. Their findings, published in Science Translational Medicine and reported on by the Wall Street Journal, indicated two ways in which antioxidant supplements might influence skin cancer growth. First, they found that the antioxidant N-acetylcysteine (NAC) doubled the rate at which malignant melanoma metastasized, or spread, to the lymph nodes of mice. Researchers also discovered that when NAC and vitamin E (another antioxidant) were inserted into human skin cancer cells grown in lab cups, the cells were better able to invade adjacent tissue. Although this seems like strong evidence against the use of antioxidant supplements, it is important to keep in mind a few considerations:

While NAC is an antioxidant, it is also an amino acid that has biological effects unrelated to its antioxidant activity. It cannot be assumed that it was NAC’s antioxidant activity specifically that caused the cancer to spread more quickly.

The researchers do not claim that antioxidant supplements cause cancer. Antioxidants protect healthy cells from free radical damage that has been linked to cancer development in the first place. At most, the study indicates that antioxidant supplements may promote the spread of cancer once it has already developed.

The study did not look at the effects of antioxidant supplements on humans. It only studied the effects of the antioxidants in mice and in cell cultures. As far as the in vitro (cell culture) findings go, there are many in vitro cancer studies (both beneficial and harmful) that end up not translating to intact animals or to humans.